Note: Descriptions are shown in the official language in which they were submitted.
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HERMOPLASTIC TUBING
Technical Field
The present invention relates generally to tubing and
particularly to fuel transport tubing such as fuel filler and fuel filler neck
tubing. More particularly, this invention relates to a thermoplastic
tubing for transfer of hydrocarbon fuel and comprises a fluoropolymer
inner layer and a melt processible polyamide outer layer wherein at
least one of the layers also includes an adhesion promoter which
improves interlayer bonding.
Background Art
Tubing assemblies for the transport of liquids and vapors
are well known in the art. In fuel-line applications, tubing assemblies
are exposed to a variety of deleterious and harmful conditions. The
tubing is in nearly constant contact with fuel and other automotive fluids
and additives. Also, there are external environmental factors such as
stone impact and corrosive media (such as salt) to consider.
This aburidance of considerations has led to design of
tubing having multiple layers. The materials of each layer have
specific, and preferably complementary, properties. Inner tubing
layers, for example, are typically designed to be resistant to permeation
by liquids and gases, while outer layers possess mechanical strength
and shock resistance.
The art contains numerous examples of multi-layer tubing
assemblies. U.S. Pat. No. 3,561,493 to Maillard discloses tubing
having two coextruded layers of different plastics, and a coextruded
layer of adhesive therebetween. The layers are chosen from plastics
having complementary properties. U.S. Pat. 4,643,927 to Luecke et ai.
discloses tubing having a central barrier layer of polyvinylidene chloride
that is relatively gas impermeable. The barrier layer is surrounded by
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inner and outer adhesive layers which in turn are surrounded by inner
and outer surface layers of polyethylene that protect the central barrier
layer from degradation. U.S. Pat. No. 5,076,239 to Brunnhofer shows
a five-layer tubing assembly having outer, inner and middle layers of
nylon, and intermediate bonding and solvent-blocking layers.
Another requirement for fuel lines is provision for
discharge of internal static electricity. Accumulated, undissipated
electric charge can eventually cause breach in a fuel line. U.S. Pat.
Nos. 3,166,688 to Rowand et al. and 3,473,087 to Slade disclose
polytetrafluorethylene (PTFE) tubing assemblies having electrically
conductive inner layers to facilitate dissipation of static electrical
energy.
More recent developments in multi-layer tubing design
have been motivated by governmental regulations limiting permissible
hydrocarbon emissions. It is known that fluoropolymers exhibit good
permeation resistance to hydrocarbon fuels. Hence, recent multi-layer
tubing assemblies have usually included at least one permeation-
resistant fluoropolymer layer. Difficulties have been encountered,
however, in finding a commercially viable design. Most fluoropolymers
having strong mechanical properties, for example, do not bond well
with other fluoropolymers. Conversely, fluoropolymers exhibiting good
bondability (polyvinylidene fluoride (PVDF, in particular) tend to be
mechanically weak.
U.S. Pat. No. 5,383,087 to Noone et al. discloses an
outer impact-resistant fluoroplastic layer, and an innermost conductive
fluoroplastic layer for dissipation of electrostatic charge. All layers are
coextruded. The innermost conductive layer exhibits an exceptional
electrostatic dissipation capacity in the range of 10-4 t~ 10-9 ohm/cm2.
Materials possessing such extremely high conductivity, however, are
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typically metallic or brittle plastic. Consequently, they
are difficult to
extrude and also exhibit poor mechanical properties. Furthermore,
most of the fluoropolymers disclosed in the '087 patent
bond poorly
with dissimilar polymers.
The fluoropolymer bonding problem is addressed in U.S.
Pat. No. 5,419,374 to Nawrot et al. Nawrot et al, disclose
multi-layer
coextruded tubing having an outer layer of polyamide 12,
an inner
PVDF layer, and a middle adhesion binder layer (a mixture
of
polyurethane and ethylene/vinyl acetate copolymer). Though,
as
discussed above, PVDF demonstrates better adhesion to the
polyamide layer, PVDF multi-layer tubing suffers from poor
cold
impact-resistance. This is due to the fact that PVDF becomes
brittle at
low temperatures.
Other high performance fluoropolymers, such as ethylene
tetrafluoroethylene (ETFE), exhibit better cold impact-resistance
but
again, have experienced bonding problems. One approach
in the art
has been to pretreat the ETFE surface using methods such
as
chemical etching, plasma discharge or corona discharge.
European
Patent Application publication No. 0 551 094, for example,
discloses a
multi-layer tubing assembly in which an inner EFTE layer
is treated by
corona discharge to enhance bonding to an outer polyamide
layer.
Similarly, PCT international application WO 68/23036 treats
an inner
ETFE layer with plasma discharge to achieve better bonding
with an
outer thermosetting elastomer layer. In the same vein,
U.S. Pat. No.
5,170,011 etches a fluorocarbon inner layer to promote
better bonding
with a polyamide outer layer. These approaches, too, have
their
problems. Pretreatment processes such as corona and plasma
discharge are expensive and can result in poor or variable
degrees of
adhesion. Furthermore, in many cases (such as with corona
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treatment), only temporary bonding is achieved and delamination may
occur with aging.
Accordingly, there is a need for an improved tubing for
trarisfer of hydrocarbon fuels that provides the necessary durability and
resistance to permeation through the utilization of a dual or multi-layer
structure characterized by increased adhesive bond strength between
the layers.
Disclosure of the Invention
The present invention is a multi-layer thermoplastic tube
for transfer of hydrocarbon fuel and comprises an inner fluoroplastic
layer and an outer polyamide layer bonded to the fluoroplastic layer
wherein an adhesion promoter is included in at least one of the layers.
The adhesion promoter is an unsubstituted or substituted phenol salt of
1,9-dizabicyclo-[5,4,0] undec-7-end which functions to increase the
adhesive bond strength between the two layers. The adhesion
promoter provides a chemically bonded adhesion in addition to the
mechanical adhesion associated with extrusion or lamination of the
layers. The adhesion promoter increases the adhesion without
adversely afFecting the electrostatic dissipation properties of the tubing
materials.
In a first embodiment of the invention, a thermoplastic
multi-layer material comprising an inner layer of a thermoplastic form of
a tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride (THV)
terpolymer and an outer layer of a melt processible polyamide bonded
to said inner layer, wherein at least one of the layers further comprises
an adhesion promoter, is provided. The adhesion promoter is an
unsubstituted or substituted phenol salt of 1,8-diazabicyclo-
[5,4,0]undec-7-ene (DBU). The multi-layer material is characterized by
increased adhesive bonding between the layers as compared to a
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multi-layer material prepared without the adhesion promoter.
In a second embodiment of the invention, a tubing for
transfer of hydrocarbon fuel ' having improved inter-layer
bonding is
provided. The tubing comprises an inner layer of a thermoplastic
form
of a tetrafluoroethylene-hexafluoropropylene-vinylidene
fluoride
terpolymer and an outer layer of a melt processible polyamide
bonded
to the inner layer, wherein at least one of the layers
further comprises
an adhesion promoter comprising an unsubstituted or substituted
phenol salt of 1,8-diazabicyclo-[5,4,0]undec-7-ene. The
tubing not only
exhibits improved resistance to delamination during forming
and
flexing, but also provides the necessary levels of impermeability
to fuel
vapors and is relatively inexpensive to produce.
In a first manifestation of the tubing of the present
invention, the tubing structure comprises an inner barrier
layer
comprising a thermoplastic form of THV and an outer protective
cover
adjacent to and surrounding the barrier layer comprising
a melt
processible polyamide and an adhesion promoter comprising
an
unsubstituted or substituted phenol salt of 1,8-diazabicyclo-
[5,4,0]undec-7-ene.
In a second manifestation of the tubing of the present
invention, the tubing structure comprises an inner barrier
layer
comprising a thermoplastic form of THV and an adhesion
promoter
comprising an unsubstituted or substituted phenol salt
of 1,8-
diazabicyclo-[5,4,0]undec-7-ene on a novolac carrier and
an outer
protective cover adjacent to and surrounding the barrier
layer
comprising a melt processible polyamide.
In a third manifestation of the invention, the tubing
structure comprises an inner barrier layer comprising a
thermoplastic
form of THV and an adhesion promoter comprising an unsubstituted
or
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substituted phenol salt of 1,8-diazabicyclo-[5,4,0]undec-7-ene
and an
outer protective cover adjacent to and surrounding the
barrier layer
comprising a melt processible polyamide and an adhesion
promoter
comprising an unsubstituted or substituted phenol salt
of 1,8-
diazabicyclo-[5,4,0]undec-7-ene.
The present invention also provides a method for
improving the bond strength between a fluoroplastic material
and a
melt processible polyamide material comprising the steps
of: providing
a fluoroplastic material comprising a thermoplastic form
of a
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride
terpolymer;
providing a melt processible polyamide; mixing an adhesion
promoter
comprising an unsubstituted or substituted phenol salt
of 1,8-
diazabicyclo-[5,4,0]undec-7-ene with at least one of the
fluoroplastic
material or the melt processible polyamide material; and
forming a
multi-layer article comprising a layer made of the fluoroplastic
material
contacting a layer made of the ;melt processible polyamide
material.
The adhesion promoter is present in an amount sufficient
to increase
the adhesive bond strength between the two layers.
The methods and compositions of this invention are
particularly useful for making multi-layer articles such
as tubing and
hoses suitable for conveying hydrocarbon fuels. The tubing,
when
employed in fuel transport hoses, provides increased inter-layer
bonding and low permeability to hydrocarbon fuel vapors.
Brief Description of the Drawings
The features of the invention, and its technical
advantages, can be seen from the following description
of the preferred
embodiments together with the claims and the accompanying
drawings, in which:
FIG. 1 is a schematic representation illustrating a method
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for producing a tubing according to one embodiment of the present
invention;
FIG. 2 is a perspective cutaway view of a tubular member
illustrating a first manifestation of the present invention;
FIG. 3 is a cross-sectional view along lie 3-3 in FIG. 2;
FIG. 4 is a cross-sectional view along line 4-4 in FIG. 2;
FIG. 5 is a perspective cutaway view of a tubular member
which illustrates another manifestation of the present invention;
FIG. 6 is a cross-sectional view along line 6-6 in FIG. 5;
FIG. 7 is a perspective cutaway view of a tubular member
which illustrates another manifestation of the present invention; and
FIG. 8 is a cross-sectional view along line 8-8 in FIG. 7.
Detailed Description of Preferred Embodiments
The present invention is a thermoplastic tube 10 suitable
for transfer of hydrocarbon fuel. The thermoplastic tube 10 of the
invention includes an inner fluoroplastic layer 12 and an outer
polyamide layer 14 bonded to the fluoroplastic layer 12. At least one of
the layers 12, 14 also includes an adhesion promoter 16 which
functions to increase the adhesive bond strength between the two
layers. The adhesion promoter 16 is an unsubstituted or substituted
phenol sale of 1,8-diazabicyclo-j5,4,0]undec-7-ene. The adhesion
promoter provides a chemically bonded adhesion in addition to the
mechanical adhesion associated with extrusion or lamination of the
layers.
The drawings and the following detailed description are
directed primarily to a two layer tubing corresponding to a preferred
embodiment of the present invention. However, it is not beyond the
scope of the invention to include one or more additional layers to
produce a multi-layer article or tubing 10 having three or more layers.
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FIG. 1 is a schematic representation illustrating the
general scheme for producing a thermoplastic multi-layer article or
tubing 10 in accordance with the present invention. FIG. 1 illustrates
an embodiment of the present invention, wherein starting materials,
including a fluoroplastic material containing an adhesion promoter and
a melt processible polyamide material, are used to form a multi-layer
article or tubing 10. Various methods known in the art can be used to
produce a bonded multi-layer article or tubing 10, wherein the inner
fluoroplastic layer 12 is bonded to the outer polyamide layer 14. For
instance, it is believed that the fluoroplastic and polyamide can be
formed by known methods into thin film layers. The fluoroplastic layer
12 and the polyamide layer 14, are co-extruded into a multi-layer article
or tubing 10.
FIGS. 2,3 and 4 illustrate a preferred manifestation of the
present invention, wherein a tubing 10 comprises an inner barrier layer
12 forming the interior wall of the tubing 10 and an outer cover 14 as
the exterior protective surface of the tubing 10. The inner layer
comprises a thermoplastic form of a THV terpolymer. The outer cover
14 comprises a melt processible polyamide and an adhesion promoter
16.
FIGS. 5 and 6 illustrate a second manifestation, wherein
a tube 20 comprises an inner barrier layer 12 forming the interior wall
of the tube 20 and an outer cover 14 as the exterior protective surface
of the tube 20. The inner layer comprises a thermoplastic form of a
THV terpolymer and an adhesion promoter 16. The outer cover 14
comprises a melt processible polyamide.
A third manifestation of the invention is illustrated in
FIGS. 7 and 8 where the tube 30 comprises an inner barrier layer 12
forming the interior wall of the tube 30 and an outer cover 14 forming
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the exterior protective surface of the tube 30. The inner
layer 12
comprises a thermoplastic form of a THV terpolymer and
an adhesion
promoter 16. The outer cover 14 comprises a melt processible
polyamide and an adhesion promoter 16.
The term "hydrocarbon" as used herein is meant to
include fuels such as gasoline, oils, air conditioning
gases, organic
chemicals, and the like.
The inner barrier layer 12 of the invention is formed from
a fluoroplastic terpolymer comprised of the monomers
tetrafluoroethylene, hexafluoropropylene and vinylidene
fluoride. The
tetrafluoroethylene-hexafluoropropylene-vinylidene fluoride
fluoroplastic terpolymer is a fluorothermoplastic such
as Dyneon THV,
which is commercially available from Dyneon. The THV terpolymer
useful in the present invention exhibits improved gasoline
permeation
resistance. Typically, the thickness of the barrier layer
12 is about 5 to
mils, preferably about 13 to 14 mils.
The outer cover 14 of the tubing is a protective layer
of a
melt processible polyamide having good heat resistance,
oil resistance,
weather resistance and flame resistance. Polyamides useful
as the
20 protective outer layer are generally commercially available.
For
example, polyamides such as any of the well-known Nylons
are
available from a number of sources. Particularly preferred
polyamides
are nylon 6, nylon 6-6, nylon 11, or nylon 12. It should
be noted that
the selection of a particular polyamide material should
be based upon
25 the physical requirements of the particular application
for the resulting
article. For example, nylon 6 and nylon 6-6 offer higher
heat resistant
properties than nylon 11 or nylon 12, whereas nylon 11
and nylon 12
offer better chemical resistant properties. In addition
to those
polyamide materials, other nylon materials such as nylon
6,12, nylon
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6,9, nylon 4, nylon 4,2, nylon 4,6, nylon 6,1 may also be used.
Polyether containing polyamides, such a PebaxT"" polyamines, may
also be used.
The adhesion promoter 16 of the present invention
improves inter-layer adhesion between the inner barrier layer 12 and
the outer protective layer 14. The adhesion promoter 16 of the
invention is an unsubstituted or substituted phenol salt of 1,8-
diazabicyclo-[5,4,0]undec-7-ene (DBU). The salt can be obtained by
adding a compound having a phenolic hydroxyl group such as phenol,
cresol or the like to DBU. The preferred adhesion promoters are salts
of phenol novolac resin with 1,8-diazabicyclo-[5,4,0]under-7-ene having
a total amine value of approximately 102 to 118 and a softening point
of about 125°C to 146°C. The adhesion promoter 16 is uniformly
dispersed within at least one of the thermoplastic THV composition or
the melt processible polyamide composition used to produce the inner
barrier layer and outer protective layer, respectively. Preferably, a
layer of the tubing modified with the adhesion promoter contains from
about 0.1 to 3 phr of the adhesion promoter.
As is common practice in the industry, one or more layers
of the tubing can be made conductive to prevent the buildup of static
electricity generated by the flow of fuel along the inner surface of the
hose. Such a build up of static electricity over time has been known to
cause the formation of pin holes in the hose allowing the fuel to leak
out through the holes. Typically, the inner barrier layer 12 or the outer
layer 14 is made conductive by compounding the layer material with
carbon black or other industry recognized ingredients to provide
conductivity to the barrier layer. While the amount of carbon black
added is not critical, excess carbon black tends to make the material
more difFicult to process. In vapor or vent applications, the innermost
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layer of the hose need not be conductive. Unlike some prior
art
methods for improving inter-layer bonding which can deleteriously
affect the electrostatic dissipative properties of the
tubing, the adhesion
promoter and processing conditions of the present invention
do not
interfere with the electrostatic dissipative properties
of the tubing.
Production of the preferred embodiment of the present
invention is as follows. First, a twin screw extruder is
used to
mix/disperse the adhesion promoter (V-13) at a concentration
of 0.1 to
3 phr with a melt processible polyamide selected from the
group
consisting of Nylon 6, Nylon 6-6, Nylo9n 11 and Nylon 12.
The
resulting composition is pellitized and used as a protective
cover or
veneer layer in a co-extruded tube over an inner THV layer.
Alternatively, a tubing incorporating the adhesion
promoter in the inner barrier layer can be produced as
follows. First,
the adhesion promoter is blended with the THV composition
at a
concentration of 0.1 to 3 phr. Then, the modified THV and
a melt
processible polyamide are co-extruded using two extruders
and a co-
extrusion die which extrudes both materials simultaneously
to form the
tubing according to another embodiment of the present invention.
One of the advantages of the thermoplastic tubing of the
present invention is that the outer layer may be directly
bonded to the
inner barrier layer without the need for an intermediate
tie layer.
Presence of the adhesion promoter in one or both layers
of the tubing
provides improved inter-layer bonding strength which produces
a tube
resistant to delamination during forming or use.
The tube of the invention may optionally include a
reinforcing member which affords physical strength to the
finished
tubing. Typically, the reinforcing member is selected from
a group
consisting of glass fibers, cotton fibers, polyamide fibers,
polyester
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fibers, and rayon fibers. Preferably, the reinforcing material is an
aromatic polyamide such as Kevlar or Nomex, both of which are
manufactured by DuPont. The reinforcing material may be either
knitted, braided, or spiraled to form the reinforcing member.
Alternatively, the reinforcing material may be chopped and added to
the nylon.
Other additives such as antioxidants, processing aids,
etc. can be employed in carrying out the present invention and it is
within the scope of this invention to incorporate herein any such
additives as commonly used in making fuel line tubing.
The THV barrier layer of the present invention is useful in
reducing the permeability of fuel vapors from the fuel transfer tube;
however, it is also useful in reducing the permeability of chemical
vapors such as in air conditioning hoses, oil hoses, and the like where
severe chemical resistance or vapor permeation resistance is required.
Having described the invention in detail and by reference
to preferred embodiments thereof, it will be apparent that modifications
and variations are possible without departing from the scope of the
invention defined in the appended claims.
